1. Field of the Invention
The present application generally relates to constant-velocity joints for aircraft rotors and specifically relates to a constant-velocity joint link having reduced stiffness.
2. Description of Related Art
Designs of rotors and propellers for aircraft are often extremely complex. A large number of factors must be taken into account, including flexure of the rotor under heavy loads and the required motions of the rotor blades with respect to the drive mechanism. The considerations for proprotors, used as both propellers and rotors in aircraft such as a tiltrotor aircraft, can be more complex than usual. A tiltrotor aircraft 11 having three-blade proprotors 13A, 13B driven by engines carried in nacelles 15A, 15B, respectively, is shown in FIG. 1.
In a gimbaled rotor, joints must be provided between the driveshaft that carries torque from the engine and the yoke that drives the blades, giving rise to a relatively complex hub assembly. An example of such an assembly used in proprotors is described generally in U.S. Pat. No. 4,804,352, assigned to Lord Corporation, which is incorporated by reference herein as if set forth in full and shown in FIGS. 2 through 5.
FIG. 2 shows a rotor assembly 17, comprising hub assembly 19 and yoke 21. Yoke 21 has three arms 23 that extend radially and are configured for rotor blades (visible in FIG. 1) to be attached thereto. Hub assembly 19 comprises an upper hub-spring plate 25, lower hub-spring plate 27, and a constant-velocity (CV) joint 29 carried between hub-spring plates 25, 27.
Referring now specifically to FIGS. 3 through 5, a drive hub 31 has a splined opening 33 for receiving a splined driveshaft (not shown), and drive hub 31 is connected through pivoting linkage to yoke 21. The pivoting linkage comprises three pairs of members, each pair having a link 35 and clevis 37. Use of these links is described in detail in U.S. Pat. No. 5,186,686, assigned to Lord Corporation, which is incorporated by reference herein as if set forth in full.
Each end of links 35 has a spherical laminated elastomeric bearing 39, 41, with the leading-end bearing 39 of each link 35 being connected to hub 31 and the trailing-end bearing 41 of each link 35 being connected to a clevis 37. Clevises 37 are connected to hub-spring plates 25, 27 with bolts 43, and bolts 43 also fasten hub-spring plates 25, 27 to each other and to yoke 21. This provides a path for torque to be transferred from the driveshaft into drive hub 31, though drive hub 31 into links 35, through links 35 into clevises 37, through devises 37 into bolts 43 and hub-spring plates 25, 27, and through bolts 43 and hub-spring plates 25, 27 into yoke 21 for driving the blades. Hub-spring plates 25, 27 cooperate to carry the thrust and shear loads for the rotor.
While the system of the present application is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the system to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the application as defined by the appended claims.